Damn, this has been a decent week for the sciences:

Members of the CMS collaboration announced the experiment’s first discovery of a new particle today.

In a paper submitted to Physical Review Letters, the CMS collaboration described the first observation of an excited, neutral Xi_b baryon, a particle made up of three quarks, including one beauty quark.

The new baryon is one of many particles made up of quarks predicted by the theory of quantum chromodynamics.

(from CMS collaboration discovers its first new particle)

Beams to order from table-top accelerators

Laser plasma accelerators offer the potential to create powerful electron beams within a fraction of the space required by conventional accelerators – and at a fraction of the cost. Their promise for the future includes not only compact high-energy colliders for fundamental physics but diminutive sources of intensely bright beams of light, spanning the spectrum from microwaves to gamma rays – a new kind of ultrafast light source for investigating new materials, biological structures, and green chemistry. Compared to today’s giant science facilities, “table-top” laser plasma accelerators may eventually be able to do equally powerful research with minimal environmental impact.

To reach these goals, laser plasma accelerators must be able to produce high-quality, stable electron beams and tune those beams to the users’ needs. The LOASIS program at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has already demonstrated high-quality beams up to a billion electron volts in a mere 3.3 centimeters; the BELLA project will reach 10 billion electron volts in a single meter.

Now the LOASIS team has demonstrated a simple way to tune highly stable beams through a wide range of energies. They describe their methods in the journal Nature Physics.

(via PhysOrg.com)

I don’t know about you, but when I think of lasers, I think of boxes on heavy, stabilized tables. Inside the boxes, the optical elements are mounted on stabilized mounts and everything is generally held as solidly in place as possible. The one thing that you generally don’t do is give a laser a good shaking. Unless it has already stopped working, in which case, have at it… preferably with a hammer.

Finding a paper that demonstrated a laser with better performance when it was being shaken compared to when it was held came as a bit of a shock.

The reason why the idea of shaking a laser is so shocking to me is that the lasers I am used to working with have optical elements that need to maintain a precise alignment with respect to one another. Temperature changes, vibrations, shaking, and “thumping the box to fix it” are all really bad ideas. But of course not all lasers are like this.

The laser in your laser pointer, CD, DVD, and Blu-Ray players are all monolithic devices. That is, they are made from a single piece of material, or materials, that are deposited on one another. You can obviously shake a laser pointer (much to the delight of cats), but this capability doesn’t scale. If you were to shake a laser pointer with acoustic waves that had a wavelength about the same size as the device (in the GHz range), then I would expect that things would probably go wrong rather quickly.

In most cases, at least. A group of researchers from Germany and Russia have now made a laser that works better when it is shaken. The reason why this occurs lies in the peculiar nature of the laser used by the researchers.

The laser that the researchers worked with was made from quantum dots (see side bar) embedded in a semiconductor material that had mirrors deposited on either side of it. This means that the distance between the two mirrors was extremely short. The researchers don’t state how big the distance was, but from the figures, I estimate that it wasn’t much longer than eight micrometers. For comparison, the wavelength emitted by the quantum dots was around 900nm.

(via A laser that works better shaken, not stirred)

Cloaking devices are one of the inventions of science fiction that have made a few tentative steps towards the real world in recent years. Now, researchers have moved the concept into the fourth dimension, creating a setup that hides a specific point in time from being perceived by observers. But if you want to make an event disappear, you have to act fast: right now, we can only hide a few picoseconds worth of time.

The cloaking devices we’ve made all work based on a similar principle: light that enters the device is bent in such a way that when it exits, its location and direction make it appear that the device itself, and anything within it, were not present. In other words, while within the device, light travels as if it were present. It’s just that, once it exits the other side, there’s no evidence that anything unusual has taken place. The same general idea governs the action of a temporal cloaking device.

The basic idea is that, when it’s not in operation, a light beam can pass through the cloaking device unhindered. When it’s switched on, a short temporal gap is opened up in the beam, then sealed back up on its way out of the hardware. One way to think of this is to view the light beam as a bit of old-fashioned magnetic tape. You can cut the tape so that a single instant of a recording can be physically separated. While separated, you can pass anything you want through the gap, but when you glue the tape back together, the recording is seamless. There’s only a before and after while the tape is cut and separated.

It’s easy to do that with tape, but a bit harder to do it with a beam of light. The key to the process is what’s being termed a split time lens, which is matched with a dispersive medium. When activated, the lens takes the light that comes before the point of cloaking and shifts it to bluer wavelengths, which travel faster through the dispersive medium than the base speed of the light in the same medium. At the cloak point, the lens switches, shifting the light beam to longer, redder wavelengths. These travel through the dispersive medium more slowly.

(via Optical setup helps researchers hide an event from time)

What’s So Interesting About Ultracold Matter?

The first of the five categories of active research at DAMOP that I described in yesterday’s post is “Ultracold Matter.” The starting point for this category of research is laser cooling to get a gas of atoms down to microkelvin temperatures (that is, a few millionths of a degree above absolute zero. Evaporative cooling can then be used to bring the atoms down to nanokelvin temperatures, reaching the regime of “quantum degeneracy.” This is, very roughly speaking, the point where the quantum wavelength of the atoms becomes comparable to the spacing between atoms in the gas, at which point the atoms become “aware” of one another.

If the atoms in question contain an even number of protons, neutrons, and electrons, then they behave as bosons, and at a particular critical temperature and density, they will suddenly “condense” into a single quantum state (generally the lowest-energy state of the trap holding them), forming a Bose-Einstein Condensate (BEC). If the atoms contain an odd number of protons, neutrons, and electrons, they behave as fermions, and cannot have multiple atoms in the same quantum state, so they form a degenerate Fermi gas, filling all the lowest-energy trap states up to some level determined by the number of atoms. In both cases, the degenerate regime is somewhere in the nanokelvin temperature range, as measured by the average energy of the trapped atoms.

Once you get matter to these ultralow temperatures, what do you do with it? There are a bunch of different things you can do once you have an ultracold gas of atoms, and in fact, this sub-sub-field is the largest single area at DAMOP, in terms of the number of invited sessions.

(via Uncertain Principles)

Laser is produced by a living cell

A single living cell has been coaxed into producing laser light, researchers report in Nature Photonics.

The technique starts by engineering a cell that can produce a light-emitting protein that was first obtained from glowing jellyfish.

Flooding the resulting cells with weak blue light causes them to emit directed, green laser light.

The work may have applications in improved microscope imaging and light-based therapies.

Laser light differs from normal light in that it is of a narrow band of colours, with the light waves all oscillating together in synchrony.

Most modern forms use carefully engineered solid materials to produce lasers in everything from supermarket scanners to DVD players to industrial robots.

(via BBC News)

The laser is a very special light source: the spatial, temporal, and frequency aspects of laser light can be exquisitely controlled. This control has enabled much of modern life, and it has had a major impact on research itself. But even the smallest laser is rather large. And many of the things we like to do with light, like imaging, are limited by the fact that normal optical elements can only focus light to a spot with a diameter that is something like the wavelength of light.

To compensate for this shortcoming, researchers have turned to the world of surface plasmon polaritons. The nice thing about plasmons is that they involve an interaction between electrons in a metal and a light field that leads to the wavelength becoming much shorter. The result is that plasmon optics are much smaller and can focus light to much smaller spot sizes. 

The dirty little secret of plasmons is that they decay away very quickly, making them tough to work with. To overcome this, researchers are working on plasmonic laser sources, called spasers.

If you’re thinking, “I’ve been here before,” you’re not wrong. In 2009, a group of researchers published the first results on a spaser. In that work, the researcher took what might be considered the chocolate-coated nut approach. Take a small gold ball and coat it in a plastic material that lases. To make the spaser go, you simply put millions of them in water and shoot a enormous laser pulse into the water—voilà, a small number of the plastic-coated gold balls will start to lase. Of course, the light goes in every direction and it isn’t much use unless you were looking for a weakly glowing cell of cloudy water. More work was certainly required.

The latest work is a natural extension of that previous effort. Instead of spheres, the researchers used gold and silver wires. These were also coated in a plastic material that could lase. Like the previous work, the researchers used another laser to excite the plastic. 

In this case, however, the details of the laser action are a little different. The plastic material absorbs light and emits photons at a lower frequency. Some of this light is captured by the wire, exciting a surface plasmon polariton that travels around the circumference of the wire. The field of the plasmon passes through the plastic material, stimulating more emission into the plasmon, increasing its intensity.

(via Ars Technica)

First Observation Of 8 Entangled Photons Smashes Entanglement Record

Entanglement is the strange quantum phenomenon in which objects become so closely linked that they share the same existence. In the language of physics, they are described by the same wavefunction.

Entangling things isn’t so difficult really. Most interactions involve entanglement of one sort or another.

The trouble is pinning it down. Entanglement is a fragile and fleeting phenomenon. Blink and it leaks into the environment. That’s why it’s so difficult to preserve, to observe and ultimately so difficult for physicists to play with.

In recent years, physicists have learnt how to entangle all kinds of objects in pairs—photons, electrons, atoms and so on. In 1999, they created a qutrit by entangling three photons. Last year, they even entangled 6 photons.

Today, however, Xing-Can Yao and buddies at the University of Science and Technology of China in Hefei, say they’ve smashed this record by entangling 8 photons, then manipulating and observing them all simultaneously.

That’s no easy feat. Getting eight photons exactly where you want them at the same time is the quantum mechanical equivalent of herding cats (clearly of the Schrodinger variety).

(via Technology Review, h/t to outofcontextscience)

Tracking photons through the classic double-slit experiment

…An exciting new experiment has been published in Science. Funnily enough, it repeats an experiment that is over 200 years old, and I am not certain that it teaches us anything new about the world. But it puts the weirdness of quantum mechanics on display for all to see. 

(via Ars Technica)

Twisty light tells left-handed molecules from right

A super twisty beam of light has been created that can distinguish between left and right-handed molecules with unprecedented precision.

Molecules often come in mirror images that can have different properties, and researchers take advantage of this “chirality” to design new drugs. They sort left from right versions using circularly polarised light, whose electric field corkscrews through space in a left or right-handed direction. Unfortunately, the technique often fails when the light’s coils are bigger than the molecules themselves.

Now Yiqiao Tang and Adam Cohen of Harvard University have created “superchiral” light that twists very tightly in places.

(via New Scientist)

wahrscheinlichkeit:

(image via insidescience.org)

Tractor beams have been a mainstay in science fiction nearly since it’s beginning, and for good reason.  The ability to directly control the movement of an object in space without physically touching it is a technology which is as elusive as it would be useful in a variety of settings.

Researchers at the Australian National University (www.anu.edu.au) have developed the first true tractor beam.  The secret to the way it works lays in the way their laser is designed.  Part of the way lasers work is the monochromatic light which is generated is in a chamber which is completely reflective.  Light jumps out of the cavity where it was born from a small puncture in this chamber.  The escaping light is collimated, forming a beam with the same diameter as the hole.  

The tractor beam uses a laser which has a donut-shaped pinhole rather than a solid pinhole.  The researchers shined the laser at a glass particle so that the particle lay inside the “hole” of the donut.  The air around the particle heated up as the laser beam was focused on it and sped up, hitting the edges of the glass particle and pushing it along the beam.  

What’s really cool about this is that if a second laser is added, researchers can make the particle effectively hover in place or push and pull it to very precise positions in space.  Australian researchers envision this technology as a new form of laser tweezer, which could be used to manipulate small particles over large distances with high precision.

(via physicsphysics)

Designer optoelectronics - quantum mechanics for new materials

European researchers have combined computer modelling of quantum mechanics and precision fabrication processes to create novel transparent conductive oxides made to order for a wide range of scientific and consumer applications.

Imagine specifying exactly how you want a new material to behave, handing those specs to an engineer, and getting back a brand-new material with exactly the qualities you need.

That’s what the EU-funded project NATCO (for Novel Advanced Transparent Conductive Oxides) set out to do. They designed and developed novel transparent conductive oxides (TCOs) to exacting specifications by applying quantum mechanics to predict a material’s optical and electronic properties, fabricating it, and checking their results experimentally.

The results? Completely new TCOs with a wide range of potential applications in sensors, solar cells, smart windows, and dozens of other scientific, commercial and consumer products.

“In the field of optoelectronics, there’s a great need to find better and less costly materials,” says Guy Garry, coordinator of the NATCO project. “The route we took was first to make calculations to find the best way to get the properties that we needed. When we fabricated these materials, we found that their properties were the same as we had calculated.”

This rational design process - using first principles to calculate the conductivity and transparency of novel materials before fabricating them - allowed the researchers to develop new TCOs with enhanced performance rapidly and efficiently.

“We were able to make these calculations very quickly, which allowed us to enhance existing properties and find new properties,” says Dr Garry.

Brand new optoelectronic material

TCOs - materials that combine transparency and conductivity, qualities that are not usually found together - have multiple applications. As sensors, photovoltaics, light emitting devices and electronically controllable films, they are found in scientific instruments, DVDs, digital cameras, mobile phones, computer displays and hundreds of other products.

Until recently, most TCOs relied on a material called ITO, an oxide of indium which is doped - slightly modified - by the addition of a small quantity of tin. ITOs have proved useful, but, Dr Garry says, suffer from two drawbacks. Their transparency is not very good, especially in the near-infrared range, and indium is in short supply and very expensive.

The NATCO team decided to explore a completely different material, strontium cuprate doped with varying amounts of barium. Copper, barium and strontium are far more abundant and much less expensive than indium.

Extensive calculations applying quantum mechanics predicted that, by doping strontium cuprate with a few percent by weight of barium, the researchers could create precisely the materials they wanted, combining good electrical conductivity and optical transparency.

Fabricating the new materials was a challenge. At first the materials were fabricated in the form of bulk ceramics and then, for actual applications, thin layers were deposited on suitable substrates.

In the end, the researchers settled on two deposition techniques - pulsed laser deposition (PLD) and metal organic chemical deposition (MOCVD). 

In PLD, a burst of laser light vaporises the material to be deposited, creating a thin film on a glass or silicon surface. It allows precise control, but can’t be used on large surfaces.

MOCVD uses organic chemistry to create gasses that deposit the desired material onto a surface. It is a more complicated procedure, but has the advantage of being able to be scaled up to coat large surfaces.

Once they had fabricated the materials, the researchers could test how well their electrical and optical properties matched the predicted values. “This was the first time that this kind of work was done on TCOs,” says Dr Garry.

Multiple applications in the works

Today, one of the most promising applications of NATCO’s new TCOs is in the area of exquisitely sensitive biosensors. These devices, with the tongue-twisting title of Elecro-Chemical Optical Waveguide Light-mode Spectroscopy Sensors, are fabricated by the Hungarian consortium partner MicroVacuum. They work by measuring how light is bent as it passes through a very thin optical wave guiding layer.

When target molecules bind to the surface of the detector, they change the TCO´s refractive index, which in turn changes how light passes through the waveguide. Applying a varying electric field through the layer provides further information about the molecules.

“We got very good results on these devices using our strontium cuprate materials,” says Dr Garry. He foresees a wide range of applications for these sensors, especially in the area of proteomics.

The project’s commercial and academic partners are pursuing other applications for NATCO’s designer TCOs, including more efficient solar cells, smart windows, novel light sources, and materials to modulate laser light.

For Dr Garry, the results of the project’s first-principles modelling and precision fabrication approach are so encouraging that he plans to apply them to more challenging problems.

“We’d like to use this route to study more complicated materials,” he says. “For example, to look at ferro-electricity to see why some materials with the same structure are ferro-electric while others are not.”

More information: NATCO project - http://www.trt.tha … co/index.htm

Provided by ICT Results (news : web)

[Source: Phys.Org]

A classical diagram of a krypton atom (background) shows its 36 electrons arranged in shells. Researchers have measured oscillations of quantum states (foreground) in the outer orbitals of an ionized krypton atom, oscillations that drive electron motion. Credit: courtesy Lawrence Berkeley National Laboratory

For the First Time Ever, Scientists Watch an Atom’s Electrons Moving in Real Time

August 4, 2010 by Paul Preuss

An international team of scientists led by groups from the Max Planck Institute of Quantum Optics (MPQ) in Garching, Germany, and from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory and the University of California at Berkeley has used ultrashort flashes of laser light to directly observe the movement of an atom’s outer electrons for the first time.

Through a process called attosecond absorption spectroscopy, researchers were able to time the oscillations between simultaneously produced quantum states of valence electrons with great precision. These oscillations drive electron motion.

“With a simple system of krypton atoms, we demonstrated, for the first time, that we can measure transient absorption dynamics with attosecond pulses,” says Stephen Leone of Berkeley Lab’s Chemical Sciences Division, who is also a professor of chemistry and physics at UC Berkeley. “This revealed details of a type of electronic motion - coherent superposition - that can control properties in many systems.”

Leone says an example of the importance of coherent dynamics is its crucial role in photosynthesis, citing recent work by the Graham Fleming group at Berkeley. “The method developed by our team for exploring coherent dynamics has never before been available to researchers. It’s truly general and can be applied to attosecond electronic dynamics problems in the physics and chemistry of liquids, solids, biological systems, everything.”

The team’s demonstration of attosecond absorption spectroscopy began by first ionizing krypton atoms, removing one or more outer valence electrons with pulses of near-infrared laser light that were typically measured on timescales of a few femtoseconds (a femtosecond is 10^-15 second, a quadrillionth of a second). Then, with far shorter pulses of extreme ultraviolet light on the 100-attosecond timescale (an attosecond is 10^-18 second, a quintillionth of a second), they were able to precisely measure the effects on the valence electrons.

The results of the pioneering measurements performed at MPQ by the Leone and Krausz groups and their colleagues are reported in the August 5 issue of the journal Nature.

Parsing the fine points of valence electron motion

Valence electrons control how atoms bond with other atoms to form molecules or crystal structures, and how these bonds break and reform during chemical reactions. Changes in molecular structures occur on the scale of many femtoseconds and have often been observed with femtosecond spectroscopy, in which both Leone and Krausz are pioneers.

                     
Enlarge

In krypton’s single ionization state, quantum oscillations in the valence shell cycled in a little over six femtoseconds. Attosecond pulses probed the details (black dots), filling the gap in the outer orbital with an electron from an inner orbital, and sensing the changing degrees of coherence between the two quantum states thus formed (below). Credit: Courtesy Lawrence Berkeley National Laboratory

Zhi-Heng Loh of Leone’s group at Berkeley Lab and UC Berkeley worked with Eleftherios Goulielmakis of Krausz’s group to perform the experiments at MPQ. By firing a femtosecond pulse of infrared laser light through a chamber filled with krypton gas, atoms in the path of the beam were ionized by the loss of one to three valence electrons from their outermost shells.

The experimenters separately generated extreme-ultraviolet attosecond pulses (using the technique called “high harmonic generation”) and sent the beam of attosecond probe pulses through the krypton gas on the same path as the near-infrared pump pulses.

By varying the time delay between the pump pulse and the probe pulse, the researchers found that subsequent states of increasing ionization were being produced at regular intervals, which turned out to be approximately equal to the time for a half cycle of the pump pulse. (The pulse is only a few cycles long; the time from crest to crest is a full cycle, and from crest to trough is a half cycle.)

“The femtosecond pulse produces a strong electromagnetic field, and ionization takes place with every half cycle of the pulse,” Leone says. “Therefore little bursts of ions are coming out every half cycle.”

Although expected from theory, these isolated bursts were not resolved in the experiment. The attosecond pulses, however, could precisely measure the production of the ionization, because ionization - the removal of one or more electrons - leaves gaps or “holes,” unfilled orbitals that the ultrashort pulses can probe.

                      
Enlarge

Femtosecond-scale pulses were fired to ionize krypton atoms (wide beam). Separately created attosecond-scale pulses (narrow beam) were absorbed by the krypton atoms. Spectroscopy mapped the precise timing of the oscillation between quantum states thus created. Credit: Courtesy Lawrence Berkeley National Laboratory

The attosecond pulses do so by exciting electrons from lower energy orbitals to fill the gap in krypton’s outermost orbital - a direct result of the absorption of the transient attosecond pulses by the atoms. After the “long” femtosecond pump pulse liberates an electron from the outermost orbital (designated 4p), the short probe pulse boosts an electron from an inner orbital (designated 3d), leaving behind a hole in that orbital while sensing the dynamics of the outermost orbital.

In singly charged krypton ions, two electronic states are formed. A wave-packet of electronic motion is observed between these two states, indicating that the ionization process forms the two states in what’s known as quantum coherence.

Says Leone, “There is a continual ‘orbital flopping’ between the two states, which interfere with each other. A high degree of interference is called coherence.” Thus when the attosecond probe pulse clocks the outer valence orbitals, it is really clocking the high degree of coherence in the orbital motion caused by ionization.

Indispensable attosecond pulses

“When the bursts of ions are made quickly enough, with just a few cycles of the ionization pulse, we observe a high degree of coherence,” Leone says. “Theoretically, however, with longer ionization pulses the production of the ions gets out of phase with the period of the electron wave-packet motion, as our work showed.”

So after just a few cycles of the pump pulse, the coherence is washed out. Thus, says Leone, “Without very short, attosecond-scale probe pulses, we could not have measured the degree of coherence that resulted from ionization.”

The physical demonstration of attosecond transient absorption by the combined efforts of the Leone and Krausz groups and their colleagues will, in Leone’s words, “allow us to unravel processes within and among atoms, molecules, and crystals on the electronic timescale” - processes that previously could only be hinted at with studies on the comparatively languorous femtosecond timescale.

More information: “Real-time observation of valence electron motion,” by Eleftherios Goulielmakis, Zhi-Heng Loh, Adrian Wirth, Robin Santra, Nina Rohringer, Vladislav Yakovlev, Sergey Zherebtsov, Thomas Pfeifer, Abdallah Azzeer, Matthias Kling, Stephen Leone, and Ferenc Krausz, appears in the 5 August 2010 issue of the journal Nature.

Provided by Lawrence Berkeley National Laboratory (news : web)

[Source: Phys.org]